Specialized drill bits are used to drill well-bores, boreholes, or wells in the earth for a variety of purposes, including water wells; oil and gas wells; injection wells; geothermal wells; monitoring wells, mining; and, other similar operations. These drill bits come in two common types, roller cone drill bits and fixed cutter drill bits.
Wells and other holes in the earth are drilled by attaching or connecting a drill bit to some means of turning the drill bit. In some instances, such as in some mining applications, the drill bit is attached directly to a shaft that is turned by a motor, engine, drive, or other means of providing torque to rotate the drill bit.
In other applications, such as oil and gas drilling, the well may be several thousand feet or more in total depth. In these circumstances, the drill bit is connected to the surface of the earth by what is referred to as a drill string and a motor or drive that rotates the drill bit. The drill string typically comprises several elements that may include a special down-hole motor configured to provide additional or, if a surface motor or drive is not provided, the only means of turning the drill bit. Special logging and directional tools to measure various physical characteristics of the geological formation being drilled and to measure the location of the drill bit and drill string may be employed. Additional drill collars, heavy, thick-walled pipe, typically provide weight that is used to push the drill bit into the formation being drilled. Finally, drill pipe connects these elements, the drill bit, down-hole motor, logging tools, and drill collars, to the surface where a motor or drive mechanism turns the entire drill string and, consequently, the drill bit, to engage the drill bit with the geological formation to drill the well-bore deeper.
A standard roller cone drill bit 202 is shown in FIG. 3. In FIG. 3, the roller cone drill bit 202 is comprised of a body 300 having a shank 302 and a plurality of legs 304. Although not shown in FIG. 3, the shank 302 has an external thread for connection to an adjacent drill string component. A bore 310 extends from the shank 302 through the body 300 of the roller cone bit 202. The legs 304 extend towards the front of the roller cone bit 202 and have a roller cone 306 disposed at an end of the leg 304. Although not illustrated, each roller cone 306 has at least one cutter disposed on an external surface of the roller cone 306 for degrading a formation. The cutters may be formed of a hardened material or have a coating of a hard material such as polycrystalline diamond. The roller cones 306 have a central axis about which they rotate, with the roller cone 306 being rotatably connected to the leg 304.
As a bore hole is drilled, fluid, typically a water or oil based drilling fluid referred to as drilling mud, is pumped down the drill string through the drill pipe and any other elements present and through the drill bit. Other types of drilling fluids are sometimes used; including air, nitrogen, foams, mists, and other combinations of gases, fluids, and mixtures of gases and fluids, but for purposes of this application, drilling fluid and/or drilling mud refers to any type of drilling fluid, including gases, fluid, and combinations thereof. In other words, drill bits typically have a fluid channel within the drill bit to allow the drilling mud to pass through the bit and out one or more jets, ports, or nozzles. The purpose of the drilling fluid is to cool and lubricate the drill bit, to stabilize the well-bore from collapsing, to prevent fluids present in the geological formation from entering the well-bore, and to carry fragments or cuttings removed by the drill bit up the annulus and out of the well-bore.
In a standard roller cone bit, drilling fluid is pumped to a working face 308 of the roller cone bit 202 through the drill string to the roller cone drill bit 202. The fluid flows through the bore 310 of the roller cone drill bit 202 to the roller cones 306 and around the roller cone bit 202. The drilling fluid returns up an annulus (the space between the exterior of the drill pipe and the wall of the well-bore). As the drilling fluid flows from the working face 308 to the outside of the roller cone bit 202, the drilling fluid carries cuttings from the formation away from the roller cone bit 202.
It may be beneficial in some situations to reverse the circulation of the drilling fluid. In such situations the drilling fluid is pumped down the annulus of the well-bore, across the face of the drill bit, and into the inner fluid channels of the drill bit through and up into the interior of the drill string. Alternatively, the drill string may have at least one section of double-wall pipe. Double wall pipe has an inner passage defined by an inner surface of the inner wall of the pipe and an outer passage defined by the outer surface of the inner wall and the inner surface of the outer wall. The drilling fluid may then be pumped down the outer passage and exit the exterior of the drill string proximate the drill bit. The drilling fluid then returns through the inner passage. It is also possible for the fluid to be pumped down the inner passage and crossover to the outer passage prior to the drill bit where the drilling fluid exits the drill string.
In either situation, the drilling fluid being pumped down the annulus or the drilling fluid being pumped down the outer passage of the double wall pipe, the drilling fluid does not necessarily pass across the face of the drill bit. Often much of the drilling fluid bypasses the face of the drill bit and flows to the inner channels of the drill bit through other paths, such as between the legs in the roller cone bit. To direct more of the fluid to the face of the roller cone bit, extensions may be welded to the roller cone bit between each of the legs. However, the process of welding the extensions may heat the bearings and seals of the roller cones affecting the longevity of the drill bit. Thus there is a need for a way to direct more of the fluid to the face of an existing roller cone drill bit without detrimentally affecting the longevity of the drill bit.